Semiconductor processing includes deposition processes such as chemical vapor deposition (CVD) of conductive, dielectric and semiconducting materials, etching of such layers, ashing of photoresist masking layers, etc. In the case of etching, plasma etching is conventionally used to etch metal, dielectric and semiconducting materials.
Showerhead electrodes for plasma processing of semiconductor substrates are disclosed in commonly assigned U.S. Pat. Nos. 5,074,456; 5,472,565; 5,534,751; and 5,569,356. Other showerhead electrode gas distribution systems are disclosed in U.S. Pat. Nos. 4,209,357; 4,263,088; 4,270,999; 4,297,162; 4,534,816; 4,579,618; 4,590,042; 4,593,540; 4,612,077; 4,780,169; 4,854,263; 5,006,220; 5,134,965; 5,494,713; 5,529,657; 5,593,540; 5,595,627; 5,614,055; 5,716,485; 5,746,875 and 5,888,907.
A common requirement in integrated circuit fabrication is the etching of openings such as contacts and vias in dielectric materials. The dielectric materials include doped silicon oxide such as fluorinated silicon oxide (FSG), undoped silicon oxide such as silicon dioxide, silicate glasses such as boron phosphate silicate glass (BPSG) and phosphate silicate glass (PSG), doped or undoped thermally grown silicon oxide, doped or undoped TEOS deposited silicon oxide, etc. The dielectric dopants include boron, phosphorus and/or arsenic. The dielectric can overlie a conductive or semiconductive layer such as polycrystalline silicon, metals such as aluminum, copper, titanium, tungsten, molybdenum or alloys thereof, nitrides such as titanium nitride, metal suicides such as titanium silicide, cobalt silicide, tungsten silicide, molybdenum silicide, etc. A plasma etching technique, wherein a parallel plate plasma reactor is used for etching openings in silicon oxide, is disclosed in U.S. Pat. No. 5,013,398.
U.S. Pat. No. 5,736,457 describes single and dual "damascene" metallization processes. In the "single damascene" approach, vias and conductors are formed in separate steps wherein a metallization pattern for either conductors or vias is etched into a dielectric layer, a metal layer is filled into the etched grooves or via holes in the dielectric layer, and the excess metal is removed by chemical mechanical planarization (CMP) or by an etch back process. In the "dual damascene" approach, the metallization patterns for the vias and conductors are etched in a dielectric layer and the etched grooves and via openings are filled with metal in a single metal filling and excess metal removal process.
During the etching process, the showerhead electrode becomes hot. In addition, the temperature can vary considerably across the surface of the electrode. The temperature difference between the center and the edge of the showerhead electrode can be about 100.degree. C. or higher, e.g. about 200.degree. C. The nonuniform temperature distribution can cause uneven plasma density and/or process gas distribution which leads to nonuniform etching of the wafer. In showerhead arrangements which are edge cooled, this problem becomes greater as the size of the substrate increases since the temperature differential between the center and the edge of the showerhead electrode will become more pronounced as the diameter of the showerhead increases.
When etching large, twelve-inch (300 mm) wafers with a showerhead electrode, controlling the process gas to create a uniform plasma distribution is made more difficult. For instance, the number of openings in the baffles and showerhead electrode must be increased significantly to obtain distribution of the etching gas over a larger area. In addition, as the number of openings in the baffles increases and the number of baffles increase, the complexity and cost to manufacture such a gas distribution apparatus increase greatly. Further, because the flow rate of the process gas must be increased in proportion to the increased surface area of the wafer, achievement of uniformity with respect to processing ratio, selectivity, feature shape and size become more difficult. Moreover, the increased size of the showerhead leads to greater temperature gradients across the showerhead which can cause uneven processing of the substrate.